Various devices or components utilize signal waveforms to measure signal values or otherwise develop data related to the signal. For example, a power detector, such as an RF (Radio Frequency) power detector, monitors a signal waveform and provides a DC (Direct Current) output voltage corresponding to the power of the signal. Power detectors are used extensively to measure and control RF signal strength in wireless systems. In transmitters, transmit power control is critical to ensure compliance with regulatory guidelines and for maintaining the range and quality of the radio link. In receivers, received signal strength is used for gain control in the RF/IF chain to maintain a constant signal level suitable for analog-to-digital conversion and demodulation.
Conventional techniques used to obtain a sample of the RF power to be monitored by the power detector include:
(1) Use of dedicated signal chains that replicate the RF signal path but with the final load or antenna replaced by a power detector. However, the implementation of a dedicated signal chain to replicate the signal path is wasteful of both power in operation and of silicon area for an RF amplifier.
(2) Sampling of a small portion of the output from the RF signal path via a directional coupler or capacitively coupled line, and sending this sampled signal to a dedicated power detector. However, this approach also consumes significant area in a device for the coupling lines, and limits placement of the coupling section within the layout of multi-stage amplifiers. Further, the coupling can be sensitive to and/or impact the impedance matching of the main signal path.
In both of these conventional approaches, after a sample or replica of the RF signal is obtained, such sample or replica is normally fed to a dedicated power detector circuit for conversion to a DC voltage. Even in a simple implementation, this requires an additional power detector device, such as a simple diode rectifier detector or NMOS (N-type Metal Oxide Semiconductor) power detector, and filtering circuitry.